i. Field of the Invention
The invention relates to an apparatus for conveying bulk material in silos, with feed means which dumps the bulk material to be introduced into the silo, and discharge means for discharging bulk material from the silo. The discharge means has a clearing unit, which works on the surface of the heap of bulk material and can be raised and lowered in the silo by means of a lifting mechanism. The clearing unit is rotatable about the vertical silo axis by means of a rotary drive. A telescopic gravity-descent tube is arranged in the silo and is provided at its top end region with a bulk-material inlet. It is coupled to the clearing unit, and follows the vertical movements of the clearing unit by being retracted and extended telescopically. The invention also extends to silos fitted with the apparatus.
ii. Summary of the Prior Art
Such apparatuses, with a telescopic gravity-descent tube standing in the heap of bulk material and forming a draw-off shaft intended for leading the bulk material to be discharged, to the silo bottom have been known for a long time for silos of small storage capacities, in particular for silos serving for receiving silage fodder or broken ice (German Auslegeschrift No. 1,250,360, German Patent Specification No. 831,519). In these known apparatuses, the clearing unit pivotable about the silo axis is mounted at the top end of the telescopic gravity-descent tube and is pivotable by mans of friction wheels which run either on the cylindrical silo wall or on the surface of the heap of bulk material. For stabilisation, there can be arranged in the telescopic gravity tube a fixed vertical tube, on which the individual tubes of the telescopic gravity tube are guided.
Apparatuses of the type mentioned above, equipped with a telescopic gravity-descent tube, have not gained acceptance in practice for bulk-material silos of relatively large storage capacities. Insofar as the telescopic gravity tube is guided by a fixed vertical tube (German Patent Specification No. 831,519), this results in a considerably increased cost of construction. At the same time there is also the disadvantage that the conveying cross-section of the telescopic tube is greatly restricted by the fixed vertical tube standing in it, while the resistance to telescopic retraction of the telescopic tube is increased adversely because the individual tube sections are guided on the vertical tube. An unsupported telescopic gravity-descent tube is known, that is to say one which is not guided by a fixed vertical tube, and instead of this, the clearing unit is supported and guided on the cylindrical silo wall by means of supporting rollers (German Auslegeschrift No. 1,250,360). When this arrangement is used, there is no guarantee of reliable vertical guidance of the telescopic tube, if only because, owing to the construction, there is a greater radial play of the clearing unit relative to the silo wall and the clearing unit running on the heap of bulk material by means of drive rollers unavoidably assumes oblique positions and, during operation, executes wobbly movements which result in tilting of the tube sections of the telescopic gravity-descent tube and consequently lead to failure of the installation.
For the storage of bulk material in silos of large storage capacity, the silos used in practice have a drawoff shaft which is arranged fixedly in the silo. The clearing unit pivots about the axis of this shaft which at the same time serves for guiding the clearing unit during its up- and down-movements (German Offenlegungsschrift No. 1,933,337, German Offenlegungsschrift No. 1,456,866, German Utility Model No. 1,968,164, German Patent Specification No. 3,135,439, German Patent Specification No. 3,151,841, U.S. Pat. Nos. 3,358,856, 2,649,215 and 772,911). In the apparatuses mentioned above, the draw-off shaft has a plurality of bulk-material inflow orifices distributed over its length and its periphery. Scraper booms, bucket chains, conveyor screws, clearing wheels and the like are used as clearing units. The arrangement of a central draw-off shaft serving at the same time for guiding the clearing units results in relatively heavy constructions involving a relatively high outlay and moreover, as regards storage materials inclined to stick and become compacted, such as, for example, gypsum, difficulties arise during the discharge operation.